1. Field of the Invention
The present invention relates to a deflection yoke for CRT apparatus, and especially relates to an improved deflection yoke to be used in an in-line type color CRT apparatus having an aspherical face panel.
2. Description of the Prior Art
Generally, a deflection yoke to be used in a color CRT apparatus having an in-line type electron gun is constituted to generate a vertical deflection magnetic field distorted in a barrel shape, and a horizontal deflection magnetic field distorted in a pincushion shape. Thereby, a self-convergence effect can be obtained in the color CRT apparatus.
Furthermore, the vertical deflection magnetic field can be partially distorted to be in a pincushion shape in a part near the phosphor screen formed on the back surface of the face panel of the CRT apparatus. Thereby a distortion of right and left raster can be corrected without losing the self-convergence effect, while the whole distribution of the vertical deflection magnetic field can be in a barrel shape.
In a conventional deflection yoke, for example, shown in Published Unexamined Japanese Patent Application Sho 59-16250. Published Unexamined Japanese Utility Model Application Sho 59-161259 or Published Unexamined Japanese Patent Application Sho 62-55851, a pair of magnetic pieces for generating a pincushion shaped magnetic field are provided on an inner surface of a vertical deflection coil near the phosphor screen. Upper and lower parts of the magnetic pieces protrude toward the outside of the coil. Such a conventional deflection magnetic yoke is known in the art, and therefore its details are not shown in the drawings.
When such a conventional deflection yoke is used in a color CRT apparatus having a spherical face panel, pincushion distortion of the raster in vertical and horizontal directions on the phosphor screen can be corrected without losing the self-convergence effect.
However, in recent years the spherical face panel of the color CRT has become progressively flatter. Therefore, the pincushion distortion of the raster becomes more apparent; even though the above-mentioned conventional technology to prevent the distortion of right and left raster is used.
FIG. 2 shows an example of the pincushion distortion of the raster appearing in the color CRT apparatus having the flattened aspherical face panel where the above-mentioned conventional deflection yoke is used. The spherical face panel has a radius of curvature at a peripheral part larger than that at a center part. When the pincushion distortion of the raster at the peripheral part is extremely larger than that at center part as shown in FIG. 2, the correction of the distortion becomes very difficult.